Cargo containers need to be inspected at ports and other points of entry or transportation for contraband such as explosives, narcotics, currency, chemical and nuclear weapons, and for cargo-manifest verification. Detection of contraband with both high detection rates and low false alarm rates is a daunting task, as these materials often have similar physical characteristics as benign cargo. The percentage of cargo to be inspected is increasing and, because of the currently manually intensive nature of inspections, so is the number of operators. Therefore, there is a need to provide an automatic detection system to reduce the number of operators, or, at least, provide assistance tools that help operators improve their throughput by scrutinizing the cargo images more efficiently, thereby increasing detection and analysis speed.
Standard and advanced X-ray systems have difficulty detecting contraband in break-bulk cargo. This difficulty is exacerbated when inspecting larger and/or cluttered pallets and cargo containers. Computed Tomography (CT) based systems have been shown to be more suitable for the difficult task of detecting aviation-threat explosives in luggage and, more recently, in larger objects.
However, existing high-energy CT systems for large objects are configured horizontally (horizontal gantry) with the object rotating around its axis. In one case, the source and detectors move vertically, and in the other case, the object moves vertically while the source and detectors are stationary. In both cases, the length of the scanned objects is limited by the system size and the configuration prevents scaling the system up to long objects such as large cargo containers and large skids.
For example, U.S. Pat. No. 5,065,418, to Heimann, describes “[a]n apparatus for inspecting articles to identify items within the articles, said apparatus comprising: means for generating a first x-ray fan beam; means for generating a second x-ray fan beam; means for moving an article to be inspected through said first and second x-ray fan beams in a direction perpendicular to said x-ray fan beams; first means for detecting radiation disposed to receive radiation from said first x-ray fan beam after penetrating said article, said first means for detecting radiation being U-shaped; second means for detecting radiation disposed to detect radiation from said second x-ray fan beam after penetrating said article, said second means for detecting radiation being L-shaped; and means for generating an image of said article from the radiation detected by said first and second means for detecting radiation.”
In addition, U.S. Pat. No. 5,091,924, to Heimann, describes “[a]n apparatus for inspecting item-containing articles for identifying the presence of items contained within the articles, said apparatus comprising: means for generating a fan-shaped radiation beam directed at an item-containing article to be inspected; means for detecting radiation from said fan-shaped radiation beam after penetrating said item-containing article and for converting the detected radiation into electrical signals; calculation means for calculating and generating an actual image of the item-containing article being inspected from the electrical signals of said means for detecting radiation; memory means for storing electrical signals comprising a reference image of said item-containing article being inspected; means for comparing said electrical signals comprising said reference image of said item-containing article with the electrical signals forming said actual image, said comparison means forming a differential image including items which are not present in said reference image; and means for displaying said differential image.”
However, the design and method of current detection system limits the depth of information that can be obtained from scanned objects. Enhanced depth information typically requires a plurality of sources. Therefore, there is a need for detection systems which are flexible and can scan objects of various sizes, while providing both depth information and images of high resolution that use a minimum amount of sources. There is also a need for scanning systems that work on reduced cost, power consumption and machine size.